Inbred corn line PHDD6

ABSTRACT

According to the invention, there is provided an inbred corn line, designated PHDD6. This invention thus relates to the plants and seeds of inbred corn line PHDD6 and to methods for producing a corn plant produced by crossing the inbred line PHDD6 with itself or with another corn plant. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line PHDD6 with another corn line or plant.

This is a continuation of application Ser. No. 07/831,031, filed Feb. 3, 1992, now abandoned.

FIELD OF THE INVENTION

This invention is in the field of corn breeding, specifically relating to an inbred corn line designated PHDD6.

BACKGROUND OF THE INVENTION

The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. For field crops, these traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and plant and fruit height, is important.

Field crops are bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant.

Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. A cross between two homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.

Corn plants (Zea mays L.) can be bred by both self-pollination and cross-pollination techniques. Corn has separate male and female flowers on the same plant, located on the tassel and the ear, respectively. Natural pollination occurs in corn when wind blows pollen from the tassels to the silks that protrude from the tops of the incipient ears.

The development of corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine the genetic backgrounds from two or more inbred lines or various other broad-based sources into breeding pools from which new inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which of those have commercial potential.

Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complement the other. If the two original parents do not provide all of the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding five or more generations of selfing and selection is practiced: F₁ →F₂ ; F₂ →F₃ ; F₃ →F₄ ; F₄ →F₅, etc.

Backcrossing can be used to improve an inbred line. Backcrossing transfers a specific desirable trait from one inbred or source to an inbred that lacks that trait. This can be accomplished for example by first crossing a superior inbred (A) (recurrent parent) to a donor inbred (non-recurrent parent), which carries the appropriate gene(s) for the trait in question. The progeny of this cross is then mated back to the superior recurrent parent (A) followed by selection in the resultant progeny for the desired trait to be transferred from the non-recurrent parent. After five or more backcross generations with selection for the desired trait, the progeny will be heterozygous for loci controlling the characteristic being transferred, but will be like the superior parent for most or almost all other genes. The last backcross generation would be selfed to give pure breeding progeny for the gene(s) being transferred.

A single cross hybrid corn variety is the cross of two inbred lines, each of which has a genotype which complements the genotype of the other. The hybrid progeny of the first generation is designated F₁. In the development of hybrids only the F₁ hybrid plants are sought. Preferred F₁ hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, can be manifested in many polygenic traits, including increased vegetative, growth and increased yield.

The development of a hybrid corn variety involves three steps: (1) the selection of plants from various germplasm pools; (2) the selfing of the selected plants for several generations to produce a series of inbred lines, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected inbred lines with unrelated inbred lines to produce the hybrid progeny (F₁). During the inbreeding process in corn, the vigor of the lines decreases. Vigor is restored when two unrelated inbred lines are crossed to produce the hybrid progeny (F₁). An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between any two inbreds will always be the same. Once the inbreds that give a superior hybrid have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained.

A single cross hybrid is produced when two inbred lines are crossed to produce the F₁ progeny. A double cross hybrid is produced from four inbred lines crossed in pairs (A×B and C×D) and then the two F₁ hybrids are crossed again (A×B)×(C×D). Much of the hybrid vigor exhibited by F₁ hybrids is lost in the next generation (F₂). Consequently, seed from hybrid varieties is not used for planting stock.

Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop high-yielding corn hybrids that are agronomically sound based on stable inbred lines. The reasons for this goal are obvious: to maximize the amount of grain produced with the inputs used and minimize susceptibility of the crop to environmental stresses. To accomplish this goal, the corn breeder must select and develop superior inbred parental lines for producing hybrids. This requires identification and selection of genetically unique individuals which in a segregating population occur as the result of a combination of crossover events plus the independent assortment of specific combinations of alleles at many gens loci which results in specific genotypes. Based on the number of segregating genes, the frequency of occurrence of an individual with a specific genotype is less than 1 in 10,000. Thus, even if the entire genotype of the parents has been characterized and the desired genotype is known, only a few if any individuals having the desired genotype may be found in a large F₂ or S₀ population. Typically, however, the genotype of neither the parents nor the desired genotype is known in any detail.

At Pioneer Hi-Bred International, a typical corn research station has a staff of four, and 20 acres of breeding nursery. Those researchers plant those 20 acres with 25,000 nursery rows, 15,000 yield test plots in 10-15 yield test sites, and one or two disease-screening nurseries. Employing a temporary crew of 20 to 30 pollinators, the station makes about 65,000 hand pollinations per growing season, and produces from three to ten new inbreds which are proposed for commercial use each year. Over the 32 Pioneer research stations in North America, this amounts to from about 100 to 300 new inbreds proposed each year from over 2,000,000 pollinations. Of those, less than 50 and more commonly less than 30 are actually selected for commercial use.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel inbred corn line, designated PHDD6. This invention thus relates to the seeds of inbred corn line PHDD6, to the plants of inbred corn line PHDD6, and to methods for producing a corn plant produced by crossing the inbred line PHDD6 with itself or another corn line. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line PHDD6 with another corn line.

DEFINITIONS

In the description and examples that follow, a number of terms are used herein. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided. ABS is in absolute terms and % MN is percent of the mean for the experiments in which the inbred or hybrid was grown.

BAR PLT=BARREN PLANTS. The percent of plants per plot that were not barren (lack ears).

BRT STK=BRITTLE STALKS. This is a measure of the stalk breakage near the time of pollination, and is an indication of whether a hybrid or inbred would snap or break near the time of flowering under severe winds. Data are presented as percentage of plants that did not snap.

BU ACR=YIELD (BUSHELS/ACRE). Actual yield of the grain at harvest in bushels per acre adjusted to 15.5% moisture.

DRP EAR=DROPPED EARS. A measure of the number of dropped ears per plot and represents the percentage of plants that did not drop ears prior to harvest.

EAR HT=EAR HEIGHT. The ear height is a measure from the ground to the highest placed developed ear node attachment and is measured in inches.

EAR SZ=EAR SIZE. A 1 to 9 visual rating of ear size. The higher the rating the larger the ear size.

EST CNT=EARLY STAND COUNT. This is a measure of the stand establishment in the spring and represents the number of plants that emerge on a per plot basis for the inbred or hybrid.

GDU SHD=GDU TO SHED. The number of growing degree units (GDUs) or heat units required for an inbred line or hybrid to have approximately 50 percent of the plants shedding pollen and is measured from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hour period are: ##EQU1##

The highest maximum temperature used is 86° F. and the lowest minimum temperature used is 50° F. For each inbred or hybrid it takes a certain number of GDUs to reach various stages of plant development.

GDU SLK=GDU TO SILK. The number of growing degree units required for an inbred line or hybrid to have approximately 50 percent of the plants with silk emergence from time of planting. Growing degree units are calculated by the Barger Method as given in GDU SHD definition.

GRN APP=GRAIN APPEARANCE. This is a 1 to 9 rating for the general appearance of the shelled grain as it is harvested based on such factors as the color of the harvested grain, any mold on the grain, and any cracked grain. High scores indicate good grain quality.

MST=HARVEST MOISTURE. The moisture is the actual percentage moisture of the grain at harvest.

PLT HT=PLANT HEIGHT. This is a measure of the height of the plant from the ground to the tip of the tassel in inches.

POL SC=POLLEN SCORE. A 1 to 9 visual rating indicating the amount of pollen shed. The higher the score the more pollen shed.

POL WT=POLLEN WEIGHT. This is calculated by dry weight of tassels collected as shedding commences minus dry weight from similar tassels harvested after shedding is complete.

It should be understood that the inbred can, through routine manipulation of cytoplasmic factors, be produced in a cytoplasmic male-sterile form which is otherwise phenotypically identical to the male-fertile form.

PRM=PREDICTED RM. This trait, predicted relative maturity (RM), is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes standard linear regression analyses and is referred to as the Comparative Relative Maturity Rating System which is similar to the Minnesota Relative Maturity Rating System.

RT LDG=ROOT LODGING. Root lodging is the percentage of plants that do not root lodge; plants that lean from the vertical axis at an approximately 30° angle or greater would be counted as root lodged.

SCT GRN=SCATTER GRAIN. A 1 to 9 visual rating indicating the amount of scatter grain (lack of pollination or kernel abortion) on the ear. The higher the score the less scatter grain.

SDG VGR=SEEDLING VIGOR. This is the visual rating (1 to 9) of the amount of vegetative growth after emergence at the seedling stage (approximately five leaves). A higher score indicates better vigor.

SEL IND=SELECTION INDEX. The selection index gives a single measure of the hybrid's worth based on information for up to five traits. A corn breeder may utilize his or her own set of traits for the selection index. One of the traits that is almost always included is yield. The selection index data presented in the tables represent the mean value averaged across testing stations.

STA GRN=STAY GREEN. Stay green is the measure of plant health near the time of black layer formation (physiological maturity). A high score indicates better late-season plant health.

STK CNT=NUMBER OF PLANTS. This is the final stand or number of plants per plot.

STK LDG=STALK LODGING. This is the percentage of plants that did not stalk lodge (stalk breakage) as measured by either natural lodging or pushing the stalks and determining the percentage of plants that break below the ear.

TAS BLS=TASSEL BLAST. A 1 to 9 visual rating was used to measure the degree of blasting (necrosis due to heat stress) of the tassel at time of flowering. A 1 would indicate a very high level of blasting at time of flowering, while a 9 would have no tassel blasting.

TAS SZ=TASSEL SIZE. A 1 to 9 visual rating was used to indicate the relative size of the tassel. The higher the rating the larger the tassel.

TAS WT=TASSEL WEIGHT. This is the average weight of a tassel (grams) just prior to pollen shed.

TEX EAR=EAR TEXTURE. A 1 to 9 visual rating was used to indicate the relative hardness (smoothness of crown) of mature grain. A 1 would be very soft (extreme dent) while a 9 would be very hard (flinty or very smooth crown).

TILLER=TILLERS. A count of the number of tillers per plot that could possibly shed pollen was taken. Data is given as percentage of tillers: number of tillers per plot divided by number of plants per plot.

TST WT=TEST WEIGHT (UNADJUSTED). The measure of the weight of the grain in pounds for a given volume (bushel).

TST WTA=TEST WEIGHT ADJUSTED. The measure of the weight of the grain in pounds for a given volume (bushel) adjusted for percent moisture.

YLD=YIELD. It is the same as BU ACR ABS.

YLD SC=YIELD SCORE. A 1 to 9 visual rating was used to give a relative rating for yield based on plot ear piles. The higher the rating the greater visual yield appearance.

MDM CPX=Maize Dwarf Mosaic Complex (MDMV=Maize Dwarf Mosaic Virus & MCDV=Maize Chlorotic Dwarf Virus): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

SLF BLT=Southern Leaf Blight (Bipolaris maydis, Helminthosporium maydis): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

NLF BLT=Northern Leaf Blight (Exserohilum turcicum, H. turcicum): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

COM RST=Common Rust (Puccinia sorghi): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

GLF SPT=Gray Leaf Spot (Cercospora zeae-maydis): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

STW WLT=Stewart's Wilt (Erwinia stewartii): Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant.

HD SMT=Head Smut (Sphacelotheca reiliana): Percentage of plants that did not have infection.

EAR MLD=General Ear Mold: Visual rating (1-9 score) where a "1" is very susceptible and a "9" is very resistant. This is based on overall rating for ear mold of mature ears without determining specific mold organism, and may not be predictive for a specific ear mold.

ECB DPE=Dropped ears due to European Corn Borer (Ostrinia nubilalis): Percentage of plants that did not drop ears under second brood corn borer infestation.

ECB 2SC=European Corn Borer Second Brood (Ostrinia nubilalis): Visual rating (1-9 score) of post flowering damage due to infestation by European Corn Borer. A "1" is very susceptible and a "9" is very resistant.

ECB 1LF=European Corn Borer First Brood (Ostrinia nubilalis): Visual rating (1-9 score) of pre-flowering leaf feeding by European Corn Borer. A "1" is very susceptible and a "9" is very resistant.

DETAILED DESCRIPTION OF THE INVENTION

Inbred corn line PHDD6 is a yellow, dent corn inbred that is best suited as a male in crosses for producing first generation F1 corn hybrids. PHDD6 is best adapted to the North-Central part of the United States. The inbred can be used to produce hybrids from approximately 70-85 relative maturity based on the Minnesota Relative Maturity Rating System for harvest moisture of grain. PHDD6 should make a very good male as it is early flowering and is high yielding for its maturity. The inbred in hybrid combination has poor stay green, is short in plant height with weak roots, and is susceptible to head smut.

The inbred has shown uniformity and stability within the limits of environmental influence for all the traits as described in the Variety Description Information (Table 1) that follows. Most of the data in the Variety Description information was collected at Johnston, Iowa. The inbred has been self-pollinated and ear-rowed a sufficient number of generations with careful attention paid to uniformity of plant type to ensure homozygosity and phenotypic stability. The line has been increased both by hand and in isolated fields with continued observation for uniformity. No variant traits have been observed or are expected in PHDD6.

Inbred corn line PHDD6, being substantially homozygous, can be reproduced by planting seeds of the line, growing the resulting corn plants under self-pollinating or sib-pollinating conditions with adequate isolation, and harvesting the resulting seed, using techniques familiar to the agricultural arts.

                  TABLE 1                                                          ______________________________________                                         VARIETY DESCRIPTION INFORMATION                                                INBRED = PHDD6                                                                 ______________________________________                                         Type: Dent      Region Best Adapted: Northcentral                              A.   Maturity: Average across maturity zones. Zone: 0                               GDU Shed: 1060                                                                 GDU Silk: 1090                                                                 No. Reps: 14                                                              B.   Plant Characteristics:                                                         Plant height (to tassel tip): 121 cm                                           Length of top ear internode: 11 cm                                             Number of ears per stalk: Single                                               Ear height (to base of top ear): 31 cm                                         Number of tillers: None                                                        Cytoplasm type: Normal                                                    C.   Leaf:                                                                          Color: Medium Green (WF9)                                                      Angle from Stalk: 30-60 degrees                                                Marginal Waves: Few (WF9)                                                      Number of Leaves (mature plants): 13                                           Sheath Pubescence: Light (W22)                                                 Longitudinal Creases: Few (OH56A)                                              Length (Ear node leaf): 56 cm                                                  Width (widest point, ear node leaf): 7 cm                                 D.   Tassel:                                                                        Number lateral branches: 18                                                    Branch Angle from central spike: 30-40 degrees                                 Pollen Shed: Heavy (KY21) based on Pollen Yield Test                           (163% of experiment means)                                                     Peduncle Length (top leaf to basal branches): 15 cm                            Anther Color: Yellow                                                           Glume Color: Green                                                        E.   Ear (Husked Ear Data Except When Stated Otherwise):                            Length: 8 cm                                                                   Weight: 15 gm                                                                  Mid-point Diameter: 33 mm                                                      Silk Color: Green                                                              Husk Extension (Harvest stage): Medium (Barely covering                        ear)                                                                           Husk Leaf: Long (>15 cm)                                                       Taper of Ear: Slight                                                           Position of Shank (dry husks): Pendent                                         Kernel Rows: Straight, Distinct                                                Number = 10                                                                    Husk Color (fresh): Light Green                                                Husk Color (dry): Buff                                                         Shank Length: 6 cm                                                             Shank (No. of internodes): 6                                              F.   Kernel (Dried):                                                                Size (from ear mid-point)                                                      Length: 6 mm                                                                   Width: 8 mm                                                                    Thick: 7 mm                                                                    Shape Grade (% rounds): 60-80 (62% medium round                                based on Parent Test Data)                                                     Pericarp Color: Colorless                                                      Aleurone Color: Homozygous Yellow                                              Endosperm Color: Yellow                                                        Endosperm Type: Normal Starch                                                  Gm Wt/100 Seeds (unsized): 14 gm                                          G.   Cob:                                                                           Diameter at mid-point: 24 mm                                                   Strength: Strong                                                               Color: White                                                              H.   Diseases:                                                                 I.   Insects:                                                                       European Corn Borer-1 Leaf Damage (Preflowering):                              Susceptible                                                                    European Corn Borer-2 (Post-flowering): Susceptible                            The above descriptions are based on a scale of 1-9,                            1 being highly susceptible, 9 being highly resistant.                     S (Susceptible):                                                                               Would generally represent a score                                              of 1-3.                                                        I (Intermediate):                                                                              Would generally represent a score                                              of 4-5.                                                        R (Resistant):  Would generally represent a score                                              of 6-7.                                                        H (Highly Resistant):                                                                          Would generally represent a score                                              of 8-9. Highly resistant does not                                              imply the inbred is immune.                                    J.   Variety Most Closely Resembling:                                          Character   Inbred                                                             Maturity    PHM81                                                              Usage       PHM81                                                              ______________________________________                                    

In interpreting the foregoing color designations, reference may be had to the Munsell Glossy Book of Color, a standard color reference.

PHM81 (PVP Certificate No. 9100095) is a Pioneer Hi-Bred International, Inc. proprietary inbred.

Data for Items B, C, D, E, F, and G is based primarily on a maximum of two reps from Johnston, Iowa grown in 1991, plus description information from the maintaining station.

ELECTROPHORESIS RESULTS Isozyme Genotypes for PHDD6

Isozyme data were generated for inbred corn line PHDD6 according to the procedures described in Stuber, C. W., Wendel, J. F., Goodman, M. M., and Smith, J. S. C., "Techniques and Scoring Procedures for Starch Gel Electrophoresis of Enzymes from Maize (Zea mays L.)", Technical Bulletin No 286, North Carolina Agricultural Research Service, North Carolina State University, Raleigh, N.C. (1988).

The data in Table 2 compares PHDD6 with its parents, PHT64 and PHG36.

                  TABLE 2                                                          ______________________________________                                         ELECTROPHORESIS RESULTS FOR PHDD6                                              AND ITS PARENTS PHT64 AND PHG36                                                                 PARENTS                                                       LOCI     PHDD6         PHT64   PHG36                                           ______________________________________                                         ACP1     4             4       4                                               ADH1     4             4       4                                               CAT3     9             9       9                                               DIA1     8             12      8                                               GOT1     4             4       4                                               GOT2     4             4       4                                               GOT3     4             4       4                                               IDH1     4             4       4                                               IDH2     6             6       6                                               MDH1     6             6       6                                               MDH2     6             6       3.5                                             MDH3     16            16      16                                              MDH4     12            12      12                                              MDH5     12            15      12                                              MMM      4             4       4                                               PGM1     9             9       9                                               PGM2     3             2       8                                               PGD1     3.8           3.8     3.8                                             PGD2     5             5       5                                               PHI1     4             4       4                                               ______________________________________                                    

INDUSTRIAL APPLICABILITY

This invention also is directed to methods for producing a corn plant by crossing a first parent corn plant with a second parent corn plant wherein the first or second parent corn plant is an inbred corn plant from the line PHDD6. Further, both first and second parent corn plants can come from the inbred corn line PHDD6. Thus, any such methods using the inbred corn line PHDD6 are part of this invention: selfing, backcrosses, hybrid production, crosses to populations, and the like. All plants produced using inbred corn line PHDD6 as a parent are within the scope of this invention. Advantageously, the inbred corn line is used in crosses with other, different, corn inbreds to produce first generation (F₁) corn hybrid seeds and plants with superior characteristics.

As used herein, the term plant includes plant cells, plant protoplasts, plant cell tissue cultures from which corn plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants, such as embryos, pollen, flowers, kernels, ears, cobs, leaves, husks, stalks, roots, root tips, anthers, silk and the like.

Duncan, Williams, Zehr, and Widholm, Planta, (1985) 165:322-332 reflects that 97% of the plants cultured which produced callus were capable of plant regeneration. Subsequent experiments with both inbreds and hybrids produced 91% regenerable callus which produced plants. In a further study in 1988, Songstad, Duncan & Widholm in Plant Cell Reports (1988), 7:262-265 reports several media additions which enhance regenerability of callus of two inbred lines. Other published reports also indicated that "nontraditional" tissues are capable of producing somatic embryogenesis and plant regeneration. K. P. Rao, et al., Maize Genetics Cooperation Newsletter, 60:64-65 (1986), refers to somatic embryogenesis from glume callus cultures and B. V. Conger, et al., Plant Cell Reports, 6:345-347 (1987) indicates somatic embryogenesis from the tissue cultures of maize leaf segments. Thus, it is clear from the literature that the state of the art is such that these methods of obtaining plants are, and were, "conventional" in the sense that they are routinely used and have a very high rate of success.

Tissue culture of corn is described in European Patent Application, publication 160,390, incorporated herein by reference. Corn tissue culture procedures are also described in Green and Rhodes, "Plant Regeneration in Tissue Culture of Maize," Maize for Biological Research (Plant Molecular Biology Association, Charlottesville, Va. 1982, at 367-372) and in Duncan, et al., "The Production of Callus Capable of Plant Regeneration from Immature Embryos of Numerous Zea Mays Genotypes," 165 Planta 322-332 (1985). Thus, another aspect of this invention is to provide cells which upon growth and differentiation produce corn plants having the physiological and morphological characteristics of the inbred line PHDD6.

Corn is used as human food, livestock feed, and as raw material in industry. The food uses of corn, in addition to human consumption of corn kernels, include both products of dry- and wet-milling industries. The principal products of corn dry milling are grits, meal and flour. The corn wet-milling industry can provide corn starch, corn syrups, and dextrose for food use. Corn oil is recovered from corn germ, which is a by-product of both dry- and wet-milling industries.

Corn, including both grain and non-grain portions of the plant, is also used extensively as livestock feed, primarily for beef cattle, dairy cattle, hogs, and poultry.

Industrial uses of corn are mainly from corn starch in the wet-milling industry and corn flour in the dry-milling industry. The industrial applications of corn starch and flour are based on functional properties, such as viscosity, film formation, adhesive properties, and ability to suspend particles. The corn starch and flour have application in the paper and textile industries. Other industrial uses include applications in adhesives, building materials, foundry binders, laundry starches, explosives, oil-well muds, and other mining applications.

Plant parts other than the grain of corn are also used in industry. Stalks and husks are made into paper and wallboard and cobs are used for fuel and to make charcoal.

The seed of inbred corn line PHDD6, the plant produced from the inbred seed, the hybrid corn plant produced from the crossing of the inbred, hybrid seed, and various parts of the hybrid corn plant can be utilized for human food, livestock feed, and as a raw material in industry.

EXAMPLE 3 INBRED AND HYBRID PERFORMANCE OF PHDD6

In the examples that follow, the traits and characteristics of inbred corn line PHDD6 are given as a line and in hybrid combination. The data collected on inbred corn line PHDD6 is presented for the key characteristics and traits.

The results in Table 3A compare PHDD6 to its PHT64 parent. The results show PHDD6 and PHT64 have similar plant height, but PHDD6 has lower ear placement. PHDD6 flowers (GDU Shed and GDU Silk) later than PHT64.

The other parent of PHDD6, PHG36, is no longer used in Pioneer breeding programs. Therefore, no data is available comparing PHDD6 to PHG36.

Table 4 compares a PHDD6 hybrid to Pioneer Brand Hybrid 3979. The 3979 hybrid has a parent in common with the PHDD6 hybrid other than PHDD6. The hybrid is adapted to much of the same area as the PHDD6 hybrid. The data shows the PHDD6 hybrid is lower yielding with lower harvest moisture, but has higher test weight than 3979. The PHDD6 hybrid is shorter with lower ear placement compared to 3979. The PHDD6 hybrid has better seedling vigor and a higher early stand count than 3979. The PHDD6 hybrid flowers (GDU Shed and GDU Silk) earlier than 3979. The PHDD6 hybrid and 3979 are similar for brittle stalk, but the PHDD6 hybrid has poorer stay green and is more susceptible to stalk and root lodging.

                  TABLE 3A                                                         ______________________________________                                         PAIRED INBRED COMPARISON DATA                                                  VARIETY = PHDD6                                                                VARIETY = PHT64                                                                                    PLT    EAR   GDU    GDU                                               VAR      HT     HT    SHD    SLK                                    DEPT       #        ABS    ABS   ABS    ABS                                    ______________________________________                                         TOTAL SUM  1        60.0   13.0  980    1030                                              2        60.0   18.0  950    970                                               LOCS     1      1     1      1                                                 REPS     1      1     1      1                                                 DIFF     0.0    5.0   30     60                                                PROB                                                                ______________________________________                                          *= 10% SIG                                                                     += 5% SIG                                                                      #= 1% SIG                                                                

                                      TABLE 4                                      __________________________________________________________________________     PHDD6 HYBRID COMPARED TO PIONEER HYBRID 3979                                   VARIETY #1 = PHDD6 HYBRID                                                      VARIETY #2 = 3979                                                              __________________________________________________________________________                 BU  BU      BAR                                                                               PLT EAR SDG EST                                             VAR ACR ACR MST PLT                                                                               HT  HT  VGR CNT                                     DEPT    #   ABS % MN                                                                               ABS ABS                                                                               ABS ABS ABS ABS                                     __________________________________________________________________________     TOTAL SUM                                                                              1   76.6                                                                               83  18.4                                                                               93.7                                                                              96.0                                                                               36.6                                                                               7.3 69.8                                            2   93.0                                                                               101 19.0                                                                               93.6                                                                              99.5                                                                               40.3                                                                               6.6 67.2                                            LOCS                                                                               35  35  40  3  23  23  31  33                                              REPS                                                                               77  77  89  6  49  49  67  74                                              DIFF                                                                               16.4                                                                               18  0.6 0.0                                                                               3.5 3.7 0.7 2.6                                             PROB                                                                               .000#                                                                              .000#                                                                              .003#                                                                              1.00                                                                              .001#                                                                              .000#                                                                              .000#                                                                              .011+                                   __________________________________________________________________________                 DRP                                                                               GDU GDU                                                                               TST GRN                                                                               STA STK RT BRT                                            VAR EAR                                                                               SHD SLK                                                                               WTA APP                                                                               GRN LDG LDG                                                                               STK                                    DEPT    #   ABS                                                                               ABS ABS                                                                               ABS ABS                                                                               ABS ABS ABS                                                                               ABS                                    __________________________________________________________________________     TOTAL SUM                                                                              1   99.2                                                                              951 990                                                                               58.1                                                                               6.5                                                                               4.3 85.5                                                                               74.5                                                                              99.4                                           2   99.4                                                                              981 1025                                                                              56.2                                                                               6.5                                                                               5.7 90.0                                                                               78.4                                                                              99.4                                           LOCS                                                                               27 10  2  40  40 12  36  9  3                                              REPS                                                                               58 21  4  89  89 23  81  20 6                                              DIFF                                                                               0.2                                                                               30  35 1.9 0.0                                                                               1.4 4.5 3.9                                                                               0.0                                            PROB                                                                               .392                                                                              .001#                                                                              .090*                                                                             .000#                                                                              .958                                                                              .000#                                                                              .003#                                                                              .347                                                                              1.00                                   __________________________________________________________________________

Deposits

Applicants have made available to the public without restriction a deposit of at least 2500 seeds of Inbred Maize Line PHDD6 with the American Type Culture Collection (ATCC), Rockville, Md. 20852 USA, ATCC Deposit No. 97410. The seeds deposited with the ATCC are taken from the same deposit maintained by Pioneer Hi-Bred International, Inc., 700 Capital Square, 400 Locust Street, Des Moines, Iowa 50309 since prior to the filing date of this application. This deposit of the Inbred Maize Line PHDD6 will be maintained without restriction in the ATCC depository, which is a public depository, for a period of 30 years, or 5 years after the most recent request, or for the enforceable life of the patent, whichever is longer, and will be replaced if it becomes nonviable during that period. 

What is claimed is:
 1. Inbred corn seed designated PHDD6 and having ATCC Accession No.
 97410. 2. A corn plant and its parts produced by the seed of claim
 1. 3. A corn plant having all the physiological and morphological characteristics of the corn plant named PHDD6, the seed of which have been deposited and have ATCC Accession No.
 97410. 4. A corn plant having all the physiological and morphological characteristics of the corn plant named PHDD6, the seed of which have been deposited and have ATCC Accession No. 97410, further having cytophasmic factors conferring male sterility.
 5. Tissue culture of regenerable cells of a plant according to claim 2 wherein the tissue regenerates plants having all morphological and physiological characteristics of PHDD6.
 6. A tissue culture of cells of a plant according to claim 5, the tissue culture selected from the group consisting of leaves, pollen, embryos, roots, root tips, anthers, silk, flowers, kernels, ears, cobs, husks, and stalks, and cells and protoplasts thereof.
 7. A corn plant regenerated from the tissue culture according to claim 5 and having the capability of expressing all the physiological and morphological characteristics of inbred corn plant PHDD6 the seed of which have been deposited under ATCC Accession No.
 97410. 8. A process for producing a hybrid corn seed which gives rise to a hybrid corn plant having alleles which, when expressed, contribute to hybrids which are adapted to the northern most corn growing regions of Canada with a CRM of between about 70 and about 85, having good yield based on hybrid maturity with good seedling vigor and early stand count, comprising the steps of:(a) planting, in pollinating proximity, seed of corn inbred line PHDD6 the seed of which have been deposited under ATCC Accession No. 97410 and another inbred line that is not PHDD6; (b) cultivating corn plants resulting from said planting until the plants bear flowers; (c) inactivating the male reproductive system prior to pollination of the plants of the female inbred line; (d) allowing natural cross pollinating to occur between the inbred lines; and (e) harvesting seeds produced on said inactivated plants of the inbred line.
 9. F₁ hybrid corn seed and plants grown therefrom produced by crossing inbred corn plant PHDD6 the seed of which have been been deposited under ATCC No. 97410 with another, different corn plant, that is not PHDD6 and plants and parts thereof produced from the F₁ hybrid seed.
 10. A tissue culture initiated from the cells of the corn plant according to claim
 9. 